How Filler Distribution Affects Paper Properties (4)

The influence of a retention aid (cationic polyacrylamide) on structure and properties of filler loaded papers was investigated. Handsheets were prepared under the following conditions:(A) without retention aid, (B) with the addition of 0.02% retention aid to the furnish, (C) preflocculated filler (containing retention aid). Geometrical parameters of filler aggregates were evaluated by image analysis of cross and parallel sections of handsheets. The results are summarized as follows:(1) The deterioration of the light scattering coefficient of handsheets containing retention aid is closely related to the decrease of z-directional count of filler aggregates.(2) A comparison between x-y directional and z-directional geometrical parameters showed that the shape of filler aggregates differs according to the condition of retention aid addition.(3) The count of filler aggregates decreases but the area of filler aggregates increases with retention aid addition. At the same time the filler aggregates tend to be located near the fiber surface.A similar study using machine-made papers was also carried out. The effects of retention aid were clearly observed in the x-y directional width and area of filler aggregates and in the degree of two-sidedness. However no influence on z-derectional count or width was observed.